This invention relates to generally to airbag closures and more particularly to invisible door arrangements that include coverings that are ruptured and pushed open by an inflating air bag to create an opening for deployment of the airbag into the passenger compartment of a vehicle.
An example of an invisible door arrangement is disclosed in U.S. patent application Ser. No. 07/975,724 filed by Robert Cooper Nov. 13, 1992 and assigned to Davidson Textron, Inc. assignee of this invention. The Cooper patent application is hereby incorporated in this patent specification by reference.
Briefly the Cooper patent application discloses an invisible door arrangement that comprises two self hinging sheet metal doors that are attached to a substrate frame, a vinyl plastic skin or shell that forms part of the decorative covering of the instrument panel, and an intermediate foam layer. The internal surface of the plastic shell is scored in an H-shaped pattern to provide weakened areas or tear lines that are ruptured to create an opening in the plastic shell when the airbag is deployed.
Invisible door arrangements of the type exemplified by the Cooper patent application are generally designed to operate in environments ranging from a low temperature of about -20 degrees fahrenheit to a high temperature of about 170 degrees fahrenheit. Many of these invisible door arrangements comprise a polyvinyl chloride (PVC) thermoplastic shell that tends to become brittle at the low temperature end. Consequently invisible door arrangements that have an outer PVC shell tend to experience some fragmentation that produces debris when the PVC shell is ruptured during airbag deployment at the low temperature end. On the other hand, a PVC shell tends to soften at the high temperature end. Consequently invisible door arrangements that have an outer PVC shell also tend to overstretch and increase the time for the tear lines to rupture when the airbag is deployed at the high temperature end.